How can I slow down the voice on my watch it talks at a high rate of speed

If the speech is fast and distorted (high pitch?) as if it is playing at the wrong speed, try a Forced Reset. Press and hold both the Digital Crown and the Side Button (together) until the Apple appears, then release and let it reboot.

Most of the speech from your watch is generated by Siri. You could try loading a different voice to force reading the sound files again. Apart from that, there is no speed control available to users, it is all in the programming and it should just work.